* bug#35222: 26.1; `read-command' documentation
@ 2019-04-10 22:13 Drew Adams
2019-04-10 22:24 ` Noam Postavsky
2019-04-11 14:02 ` Eli Zaretskii
0 siblings, 2 replies; 6+ messages in thread
From: Drew Adams @ 2019-04-10 22:13 UTC (permalink / raw)
To: 35222
1. The doc string does not say what happens if DEFAULT is not provided
(so `nil') and the user enters empty input. And what happens is not
obvious. Please add that information to the doc string.
2. What does happen? Well, it's documented in (elisp) `High-Level
Completion'. But please add information to that Info node that helps
users understand a return value that is an empty-named interned
symbol, which has the print and read syntax `##'. It's pretty
unusual for the default behavior of a read command to return such an
odd beast. (The default behavior is the case when arg DEFAULT is
absent, hence `nil'.) And please provide a cross-reference to node
`Symbol Type', which explains this syntax.
User code that tests the result of `read-command' typically needs to
deal with the default DEFAULT case, hence with the possibility of the
function returning an uninterned symbol. Users need to be aware of
this possibility - it's a gotcha.
In GNU Emacs 26.1 (build 1, x86_64-w64-mingw32)
of 2018-05-30
Repository revision: 07f8f9bc5a51f5aa94eb099f3e15fbe0c20ea1ea
Windowing system distributor `Microsoft Corp.', version 10.0.17134
Configured using:
`configure --without-dbus --host=x86_64-w64-mingw32
--without-compress-install 'CFLAGS=-O2 -static -g3''
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#35222: 26.1; `read-command' documentation
2019-04-10 22:13 bug#35222: 26.1; `read-command' documentation Drew Adams
@ 2019-04-10 22:24 ` Noam Postavsky
2019-04-10 23:32 ` Drew Adams
2019-04-11 18:55 ` Stefan Monnier
2019-04-11 14:02 ` Eli Zaretskii
1 sibling, 2 replies; 6+ messages in thread
From: Noam Postavsky @ 2019-04-10 22:24 UTC (permalink / raw)
To: Drew Adams; +Cc: 35222
On Wed, 10 Apr 2019 at 18:14, Drew Adams <drew.adams@oracle.com> wrote:
>
> 1. The doc string does not say what happens if DEFAULT is not provided
> (so `nil') and the user enters empty input. And what happens is not
> obvious. Please add that information to the doc string.
Um, can we declare the current behaviour a bug, and instead return nil
in this case? That matches the current doc string (i.e., return
DEFAULT-VALUE), and avoids the whole mess with the empty string symbol
which is weird and pretty useless as far as I can tell.
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#35222: 26.1; `read-command' documentation
2019-04-10 22:24 ` Noam Postavsky
@ 2019-04-10 23:32 ` Drew Adams
2019-04-11 18:55 ` Stefan Monnier
1 sibling, 0 replies; 6+ messages in thread
From: Drew Adams @ 2019-04-10 23:32 UTC (permalink / raw)
To: Noam Postavsky; +Cc: 35222
> > 1. The doc string does not say what happens if DEFAULT is not provided
> > (so `nil') and the user enters empty input. And what happens is not
> > obvious. Please add that information to the doc string.
>
> Um, can we declare the current behaviour a bug, and instead return nil
> in this case? That matches the current doc string (i.e., return
> DEFAULT-VALUE), and avoids the whole mess with the empty string symbol
> which is weird and pretty useless as far as I can tell.
Good question. That was in fact my first reaction.
I wrote the bug report that way, then reconsidered.
I agree that the behavior is weird, and I'm not sure
what users, in what use cases, it could help. IOW,
why?
But the behavior has apparently always been thus.
(Prior to Emacs 24 there was no such read/print
syntax for uninterned symbols, so it was arguably
even weirder. If you used the result as a variable
value and did `C-h v' it would show you nothing!)
I ended up figuring that someone wanted this for
some good reason that I couldn't think of, and that
since it is documented this way (always returns a
symbol) and it is of long date we should just leave
it and make sure the doc string also helps.
But it sure is a gotcha. Why the default DEFAULT
behavior would be something so unexpected is a
good question. Hysterical accident? Intentional
design? Anyone know or have an idea what good this
is?
All I could think of is that code using it can be
sure to get a symbol. But it sure isn't sure to
get a command... I don't have the C sources, but
a priori (e.g. if I were writing `read-command'
from scratch in Lisp) it seems like it should
_require_ a commandp symbol, i.e., use
`completing-read' with non-nil REQUIRE arg.
Someone is sure to enlighten us. When that happens,
and if the decision is to continue the behavior,
hopefully people will agree even more strongly with
the need to provide clear doc about this odd default
case.
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#35222: 26.1; `read-command' documentation
2019-04-10 22:13 bug#35222: 26.1; `read-command' documentation Drew Adams
2019-04-10 22:24 ` Noam Postavsky
@ 2019-04-11 14:02 ` Eli Zaretskii
1 sibling, 0 replies; 6+ messages in thread
From: Eli Zaretskii @ 2019-04-11 14:02 UTC (permalink / raw)
To: Drew Adams; +Cc: 35222-done
> Date: Wed, 10 Apr 2019 15:13:31 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
>
> 1. The doc string does not say what happens if DEFAULT is not provided
> (so `nil') and the user enters empty input. And what happens is not
> obvious. Please add that information to the doc string.
Thanks, fixed.
> 2. What does happen? Well, it's documented in (elisp) `High-Level
> Completion'. But please add information to that Info node that helps
> users understand a return value that is an empty-named interned
> symbol, which has the print and read syntax `##'. It's pretty
> unusual for the default behavior of a read command to return such an
> odd beast. (The default behavior is the case when arg DEFAULT is
> absent, hence `nil'.) And please provide a cross-reference to node
> `Symbol Type', which explains this syntax.
Done.
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#35222: 26.1; `read-command' documentation
2019-04-10 22:24 ` Noam Postavsky
2019-04-10 23:32 ` Drew Adams
@ 2019-04-11 18:55 ` Stefan Monnier
2019-04-12 0:11 ` Noam Postavsky
1 sibling, 1 reply; 6+ messages in thread
From: Stefan Monnier @ 2019-04-11 18:55 UTC (permalink / raw)
To: Noam Postavsky; +Cc: 35222
>> 1. The doc string does not say what happens if DEFAULT is not provided
>> (so `nil') and the user enters empty input. And what happens is not
>> obvious. Please add that information to the doc string.
> Um, can we declare the current behaviour a bug, and instead return nil
> in this case? That matches the current doc string (i.e., return
> DEFAULT-VALUE), and avoids the whole mess with the empty string symbol
> which is weird and pretty useless as far as I can tell.
Yes, it would seem to be more in line with the usual expected behavior.
The caller can get the current behavior by passing ## as the DEFAULT
argument, so there doesn't seem to be any good reason to return ## when
DEFAULT was nil.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#35222: 26.1; `read-command' documentation
2019-04-11 18:55 ` Stefan Monnier
@ 2019-04-12 0:11 ` Noam Postavsky
0 siblings, 0 replies; 6+ messages in thread
From: Noam Postavsky @ 2019-04-12 0:11 UTC (permalink / raw)
To: Stefan Monnier; +Cc: 35222
Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
>>> 1. The doc string does not say what happens if DEFAULT is not provided
>>> (so `nil') and the user enters empty input. And what happens is not
>>> obvious. Please add that information to the doc string.
>> Um, can we declare the current behaviour a bug, and instead return nil
>> in this case? That matches the current doc string (i.e., return
>> DEFAULT-VALUE), and avoids the whole mess with the empty string symbol
>> which is weird and pretty useless as far as I can tell.
>
> Yes, it would seem to be more in line with the usual expected behavior.
> The caller can get the current behavior by passing ## as the DEFAULT
> argument, so there doesn't seem to be any good reason to return ## when
> DEFAULT was nil.
Since this bug is already closed, this should go Bug#35231.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-04-12 0:11 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-04-10 22:13 bug#35222: 26.1; `read-command' documentation Drew Adams
2019-04-10 22:24 ` Noam Postavsky
2019-04-10 23:32 ` Drew Adams
2019-04-11 18:55 ` Stefan Monnier
2019-04-12 0:11 ` Noam Postavsky
2019-04-11 14:02 ` Eli Zaretskii
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